Telephone-exchange system.



A. E. KEFT'H.

i 'THEPHONE EXCHANGE SYSTEM.

APPLICATION "min MAY 14, 19.01.

Patented Feb. 20,1917.

A. E. KEITH. I TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED HAY 1'4. 1901.

' Patented Feb 20,1917

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1 IELEPHONE EXCHANGE SYSTEM.

' 1o SHEETS-SHEET 4.

Patented Feb. 20, 1917.

APPLICATION FILED "HAY I4- 1901.

A. E. KEITH. TELEPHONE EXCHANGE SYSTEM.

Patented Feb. 20, 1917.

1 APPLICATWN F ll-ED IIAY H. 1901.

10 SHEETHMHI.

A. E. KEITH TELEPHONE EXCHANGE SYSTEM APPLICATION FILED IAYI4 190T tented Feb 20,1917

I0 Kim's-SH ET I A. E. KEITH. TELEPHONE EXCHANGE SYSTEM.

APPLICATION. FILED MAY H, 1907.

' Patented Feb. 20,1917.

% b Pb A. E.KEITH. TELEPHONE EXCHANGE, s'ysIEm.

APPLICATEON FILED IAY HI 1907- Y Patented Feb;'20,1917.

A. E. KEIT'H. TELEPHONE sxcmucs SYSTEM. [D MAY. 1907- Patented Feb 20 1917 AMER ea ifi toms,

and resident of Chicago, nois', have invented acertam new 'tion; the provision condition, and

ALEXANDER E, KEITH, UF CHICAGO, ILLINOIQASEIGNOB, BY

unsmi assmuunm's, "r0

AUTOHATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A COBFOM'I'ION OI ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.-

Speclflcation of Letter: Intent.

Patented FeE Application filed Kay 14, 1907. Serial 1W0. 878349.

To all whom it may concern:

Be it known that I, ALEXANDER E. Knrm, a citizen of the. United States of America,

Cook county, Illiand useful Improvement in Tele hone-Exchange Sys of which the following is a specification. f

My invention relates to tele hone systems in general, but more particu arly to automaticor semi-automatic telephone exchange systems, and especially to systems in which either all or a portion of the general operation of connecting calling telephone lines with called lines is accomplished automati' cally-that is to so by means of selecting or connecting switc es controlled from some distant point, as distinguished from ordi nary manual switch-boards. Generally stated the object my invention is the provision of an improved and hi hly eflicient telephone exchange system.

-%p'ecial objects are the provision of means whereby the connectors or final numerical switches may be considerably reduced in number, without reducing the efiiciency .of

'the service; the provision of a novel arran ement whereby each subscriber is provi ed with two individual trunking switches, one by which the subscriber calls other subscribthe' subscriber is called by other subscribers; the provision of a novel and efficient arran ment by which intermediate non iiuitleiioa tlunlt selectors are employed for automatically selecting idle numerical switches, such as connectors or other similar switches; the provision of an arrangement by which, after several switches have been brought into service to extend connection from a'calling subscribers line to a called subscribers line, one or more of. such switches may then beautomatically cut out and restored to normal the subscribers lines connected-for conversacontrolled and brought into service by the calling-subscriber for the purpose of extend-t:

ing connection t one or more of in the directionof; the calling subscriber,- the.

ondary or trunking line switch line switch K;

condition, leaving sub-central of means whereby, after a plurality of automatic switches have been 1 eat diagrammatically the; wlw o the called subscribers line said switchesmay be auto matically cut. out and restored to normal a new or substitute connection. extended back from the called telephone line or practica simultaneous'with the estab lishment of the new or talking connection; 4

or temporally connection being'simultaneous and the provision of certain details and .fea-

tures of improvement and combinations tending to increase the general efii particular (1 aracter.

To the foregoing and other useful ends, I provide certain features of construction and novel arrangements which constitute a substantial contribution tothe general art of telephony, particularly the art of automatic telephony, and which point the way to a new line of development as will hereinafter more fully a pear.

In t e accompanying drawings Figure 1 represents diagrammatically a subsc'ribers su station A and itsallotted line-switch C, with the master switchflD, a battery B hav eiency and serviceabilit of a telephone system of this ing its positive terminal grounded at'lG, provided for operating the line and master switches. I

Fig. 2 shows diagrammatically a'l'first-sm lector switch E and a second-selector switch F, in connectionwith which I have elected to explain my invention.

Fig. 3 shows nector switch H of an improved t pe,.a sectogether with its master switch J Q r Fig. 4 shows a called subscribers substation A connected 'with the outgoing line switch C,'and alsolvith' a second or incoming line switch K of an improved type.- The switch 0 is controlled by the master switch L, while the master switch M controls the Figs. 1,2, 3 and 4 taken togetheryrepresent diagrammatically the" switching -appadiagrammatically a conratus involved in tablishin Cal-connection between a. subscriber {of t e, subZ-central #1100, for example, and a subscriber of th, #2200. *Ihe subcentral nppa' ratus is represented in Fig sQl, B and a, mail Fig. 2 re' resents thema1n"central iga 3,.3 an'd' 4 taken to e 3 and 4, respectively, like parts being similarly shown and bearing the same reference numerals.

Fig. 5 is a more complete diagrammatic re resentation of the line switch (I).

Tig. 5 is a detailed view of the construction. of the bank 0 of the master switch 1).

Figs. 0, 7, 8, 9, 10,11 and 12 are detail views showing the various positions of the im'mlse springs.

i i 13 shows, in a general manner, the. relative locations of the different switches em 'loyed'in the system.

he subscriber of the sub-central #1100 may call and signal any subscriber oi' the sub-centrals #1200, #2200 and #3300 (Fig.

13) through the. medium of the. main central exchange. Also, if the sul )scriber at substation A of the sub-central #1100 desires to call another subscriber of the same sub-central, the. connection is extended to the main exchange and then back to the subcentral #1100 to the desired substatiim. In a similar manner, the subscribers of the subcentrals #1200 and-#2200 may extend connection to other substations, the connection always extending through the'maiu central exchange,evenwhen the. calling and called subscribers are members of the same subcentral exchange. But in the sub-central '#3300-tl1e arrangement is such that the sub-- Scribers may call other subsc'zibers of the same sub-central, without operating the main central switching apparatusthat is, the subscriber at sub-station A of the subcentral #3300 may call and signal the subscriber at substation A entirely by means I cam-arm 4.- momentarily presses the release,

of switching apparatus located at the sub central #3300, while the-subscribers at subccntrals #1100, #1200 and #2200, in calling other subscribers of the same. sub-central, operate switching apparatus located in the main exchange and also in the sub-reutral exchange. Furthermore, the subscribers of sub-centrals #1100, #1200 and #2200 may automatically call any subscriber of the system, but the subscribers at the subcentral #3300, when they desire connection with a line outside of their own sub-central, signal-anoperator at the #3300 sub-central,

and the operator, by means of a calling dc..-

vice, in turn completes the connection. with the desired line.

' The substations are all alikeand may be of any suitable or approved type. The. sub-- station A, for example, comprises a receiver 2, a switch-hook for controlling the substa-' tion circuits, which controlling operations are accomplished through the medium ofany suitable means, such as the cam-arms 4, 5 and 6. As the sw|tch-hook1s lowered the springs 7, 8 and 9 into engagement, wliercby the substatlon line conductorsmay begrounded simultaneously .when the springs 18 and 19 are in contact for the purpose of? releasing the switching apparatus at the central ofiice. When the. switch-hook is down the cam-arm 5 engages the spring 10, thereby bridging the ringer 11 in series with the. condenser 12 across the. line. Furthermore, when the switch-hook is down the sail camarm discngages the springs 13 and H, thus breaking the local circuit which includes in series the. primary winding 15, transmitter 16 and local battery 17. The substation ground circuit is normally broken between the ground springs 18 and 19 by the camarm 6; but when the said springs are together ground is provided to the ground post 20, and to the release spring 7, as is usually the case in telephones of this type. The said substation comprises the usual induction-coil 21 having the primary winding 15 and the secondary winding 22.- Being an automatic substation it is also provided with the usual and so-called verticalandrotary impulse springs 23 and 24:. Said substation is, of course, provided with a dial (not shown) which is secured to the shaft 25, together with the locking dog 26. Thesubstw tion A, as shown in Fig. 1,- is seen from the back, the dial being on the opposite side. Furthermore, there is a locking cam 27 that locks the dog 26 while the receiver is on the switch-hook, to prevent a rotation of'the dial. For operating the impulse springs 23 and24 the substation is provided with an impulse wheel 28 that is secured to the shaft,- whi'ch impulse wheel carries on its periphery the so-called vertical impulse teeth 29 and one rotary impulse tooth 30. The said impulse teeth are so arranged that when the dial is drawn down the impulse spring 23 is not carried into contact with the ground post 20, while the rotary spring is ope-rated once by the rotary tooth 30 but as the dial returns, one or more. of the vertical teeth engage the vertical impulse spring 23 and press it onto the said ground post 20, and after they have completed their work the. rotary impulse tooth 30, in a similar manner, again. operates the rotary impulses wing 24. In this operation the subscribers rotary line conductor is first given one preliminary ground impulse and then the vertical line conductor 31 is' given a number of ground impulses, after which the rotary line conductor 32 is given one more ground inn'mlse. It will be noticed that. as long as the dial is out of normabposition the construction is such that the dog 20 permits the secondary circuit springs 33 and 34 toseparate, thus preventin the impulses that are deliveri-al to either ine conductor from passing to the. other. The vertical-impulse spring 2 is provided with an oblique projection or'lug (Fig. 7'

post 20. The rotary impulse spring 241 is 1 provided with somewhat similar mechanism.

for driving the said rotary spring-onto the ground post, once when the'dial isrotated in and once when rotated in the one direction,

opposite direction. The said rotary impulse spring 2 L has onits under side a V-shaped member 269 having two sides and d, and there is in addition an auxiliary spring 270 which works in conjunction :with the said V-shaped member. As shown more clearly in F i .6 the auxiliar s rin 270 is .rovided g Y P g P with a lower curved parte having the rear section 271 curving outwardly, as shown also in Figs. 7, 8, 9, 10, 11 and 12. The front section 272 of said member a is designed to fall just below the apex of the V-shaped member 269, so that the rotary impulse tooth 30, when moved in the direction of the arrmv will pass onto the curved member e, thus pressing the rotary impulse spring 24' onto the ground post for a comparatively longtime, as shown in Fig. 8, and thus sending to the line a comparatively long impulse. As the impulse wheel advances, the vertical. impulse teeth 29 approach the lug 268 oi. the vertical impulse spring (Fig. 8), and eventually the first tooth j that meets the lug 268 olearsthe said lug, as shown in Fig. 9, but not until after the rotary impulse tooth 30 clears or disengages the curved member 0. As the impulse wheel continues 0 advance in the direction of "the arrow Fig. 9), succeeding impulse teeth. 29 will ,lc ar the pro ection 268, as shown in Fig.

leased, first the vertical impulse spring 23, which the vertical impulse teeth previously cleared, is carried into engagement with the groundpost 20, as indicated in Fig. 1.1; and

ber 269 directly, but for a-short time only,

sending the ordinary impulse, through the mediliim of the rotary impulse spring 2.4, to

I the line conductor 32, after which the said I member 269 IS cleared, as shown In F1g. 7

as thelmpulse wheel reaches its normal position; The operations, as thus described, are repeated each time'that the dial isoperated,

and the number of impulses produced through themedium of the vertical im ulse spring 23 are accurately and definitely eterini ned at each operation of the dial by the finger-hole which the subscriber previously selects on the dial. Means whereby the;s11b-..

scriher may signal the called subscriber comprises the push-button spring 35 which 1101.

.mally engages the contact point 36'; but

when the button 3'? is pressed the spring 35 engages the contact point 38, whereby -the vertical. line conductor 31 mav be grounded.

Such a substation described in United States Patent application of John Erickson,

.Serial No. 343,043, filed December 21, 1906.

switch-release magnet 49, all of which are built about a switch-base or frame (not shown) of any suitableor approved desi n.

The said switch-release magnet is provi ed with an armature 49 that-is pivoted on a pin 50 which rises from the base of the switch. The said armature carries pivotally secured on its end a second armature 51 that is controlled by the trip magnet 47. The pin 52 about which. the armature 51 oscillates is carried on the end of the armature 49. The plunger 44 pivotally secured by the pin to the plunger arm 45', which latter is in turn pivoted to a pin 54 that rises from the switch-frame. The lug 55 is stamped out of the side of the frame and is provided as a stop or rest for the armature-49. Upon the armature 51 is secured the catch sprin 56 which is adapted to engage the end 5 of the plunger arm #15. Furthermore, the said line switch is provided with a bank of terminals, usually ten. in number, only one of which is shown at Q (Fig. 5). As shown, the said terminal Q is, for convenience of illustration, rotated from its true position with respect tothe swing of the plunger 44, and the bushing 62 is correspondingly arranged, all for the purpose of making the illustration clearer. The terminal Q comprises the springs fi3 and (H, (35 and (i6, (i7

\Vhen'tho armature 51 is attracted thecatch .56 slides out of contact with the end 570i the plunger arm 45, and the said plunger I arm 45, .owing to the tension offitlie sprlng 58,'mjoves about the pin 5-1 and thrusts the plunger 44 into the bank terminal Q, (shown in Fig. 5i z. and when the trip magnet again .deiinergizes, theftrip armature 51 falls against theend of the plunger arm 45. The switch is restored "when the release magnet 48 becomes energized, whereby the armature 49 is attracted, and accordinglythe'" trip closed hereinafter.

armature 51 is moved upwardly until the" catch 56 slidesover the end 57; then when the release magnet 4-8 becomes deenergized the armature l9 returns to normal position and remains at rest against the stop 55. l urtlwrmore, since the plunger arm 45-is now in engagement with the armature 51, the said plunger arm is also moved about the pin 54, whereby theplunger +1 is moved from the terminal Q and falls back into the trough 1 of the plunger-shaft; and as the said plungershaft is advanced each time an idle trunk line is seized, the idle plungers are then advanced to point opposite the next idle trunk line. 4+ is carried along by the shaft )0 until it is again released when another call is made.

The master switch D, which may be of any suitable or approved type, is provided for operating the plunger shaft 60, and for controlling cei'tain circuits that will be dis- It comprises the following details: A motor magnet 71 for operating the ratchet wheel 72, which latter is designed for operating the plunger shaft ($0, and a differential relay 73 for controlling the energizing circuit of the motor magnet 71. The said master switch also has a bank 0 comprising a plurality of individual contact segments a and a common metallic segment 74, as shpwn in Fig. 5. The wiper 75 is adapted to remain in constant engagement with the bank 0, and to maintain some one of the segments a in electrical connection with thecommon segment 74. The wiper 75 is, operated in a step-by-step manner by the ratchet wheel 72 through the medium of a cammember 76 rigidly secured to the said wiper 75 and adapted to suecessively engage the pins 77, 78, 79 and 80 upon the said ratchet wheel 72. The motor magnet 71 is provided with an armature 81 upon the endof which there is suitably secured a pawl 82. Each time that the said magnet is energized the pawl 82 engages the ratchet wheel 72, advancing the latter one step. It will be noticed, therefore, that as the ratchet wheel 72 advances in a counterclockwise direction the wiper 75 advances step bystep from right to left, and when the. pin 77, for instance, clears the cam 76 the retracting spring 83 restores the. wiper 75 to its first position at the right of the. bank 0, and in engagement with, the first segment 84. The said motor magnet 71 is provided with a couple of interrupter springs 85 and 86 that are included in the energizing circuit of the said motor magnet, which energizing circuit also comprises the springs 87 and 88 controlled by the diflong as the differential relay 73 remains en- 'terminal of the line switch bank.

From this on the plunger ergized. Also, it is assumed that the terminal Q of the line switch C is the first The plunger 44, while in normal locked engagement with the shaft 60, is retained in front of said terminal by the plunger shaft 60 whenever the master switch wiper 75 is in engagement with the bank segment 84; but as the lnotor magnet 71 advances the wiper 7 5 onto the second segment 89, the said plunger and all idle plunger-s similarly engaging the shaft (50 are carried opposite the next terminal of the line switch bank. The master switch bank 0 (Fig. 5) comprises the individual segments a separated from the common segment 7 by the insulating strip 273. It will be noticed that after the wiper 75 passes over the segments from right to left and engages the last segment 164, then on the next step the wiper 75 passes from the extreme left contact 164 to the contact 84 on the extreme right; but in passing from one extreme position to the other the upper part of the wiper 7 5 slides onto the insulated member 274. This'provisi'on is made in order that the individual segments a may not be brought into contact with the common segments, whereby some interference with the successful operation of the master switch might be experienced. It should be noted that in each switch bank all of the. springs 63 are permanently connected and may be made of one common piece; the springs 64, however, are individualthat is, there is one separate and distinct spring for every-terminal Q, there being ten in the bank. The springs 65, 67, 68 and69, like the springs 63, are also common, and the springs 66 and 70, likethe springs 64, are individual. For every bank terminal Q, there is a trunk line of three conductors 90, D1 and 92 leadingto a second-selector; and there is also a normal trunk line comprising the conductors 93, 9 and 96 leading to'the incomingline switch and a conductor 9:) leading to the connector switch banks. The subscribers line conductors 31 and 32 terminate in the springs 63 and 65 which, as has been stated. are common springs. When the subscriber operates the line switch C and the plunger 44. engages the terminal Q, the subscribers line conductors 31 and 32 are extended to the vertical and rotary trunk conductors. 90 and 91 and thence to the switch E.

The selector E, shown in Fig. 2. is a modificd form of the selector switch disclosed in United States Letters Patent No. 815,321T, granted'hlarch 13. 1906, to Keith. Erickson and rlrickson. cal magnet 96 and a rotary magnet 97, a release magnet 98 and a private magnet 99. The said'private magnet 9. of course, controls the side switch wipers 100, 101, 102 and 103, the said private magnet also control- It is provided with a verti- I 45 selector ling' the circuit of the vertical magnet 96 in theusual manner by means of the spring 105 and 106, but not the circuit of the release ma et, for the release magnet spring is omitted. The vertical movement of the switch shaft and, therefore, of the wipers 119,120 and 121 is controlled by the verticalm'agnet 96, and therotary movement by the rotary magnet 97, the rotary magnet 1 circuit being provided with the usual interrupter sprin 107. The operating magnets of 1 the switc are, of course, controlledb the subscriber through the used the vertlcaland rotary line relays 108 and 109, as is well known. Saidrelays have under their control the usual springs 110,111 and 112 and in addition the trunk-release springs 113 and- 114, whereby the'said switch may bereleasedwhen the side switch wipers are in first or second position. By means of the back-release relay 115 the release of the switch E is brought about after the side switch haspassed to third position. Eachselector switch in this system is pro- .35 vided with line and private banks. The contacts of each line, bank are adapted to be engaged by corresponding line wipers, such as the wipers 119 and 120, and the contacts of each private bank by a corresponding'privatefwiper, such as the wiper121.

The selector 'F is. also a modified form of the selectorpof the said selector patent. It is of-tlie bridging type, in which the line re.- a lays 188 an .206 are permanently connected to theside switch wipers 187 and 263.

It is also prqvidedwith the vertical magnet 264' and the rotary magnet 65, the release magnet 248 ;and the priva magnet 123. The linerel'iiys 18S and 206, as shown, con trol the so-called trunk-release springs 122 and254, the former being connected with the trunk-release conductor 104, and thelatter with the release magnet 248; The pri- 'vate ma et 123 of the switch F, unlikethe is provided with the usual spring 124 that is connected with the release'm'agnet248.

V v The connector switch may also be of any suitable. or approved type, and, as shown, is a modified form of'theconnector' described in United States Letters Patent No. 815,176.,- granted March 13,|'1906,' to' Keith, -Erickson and Erickson. he connector, switch shaft (not shown). like the first-"selector. switch shaft, carries the wipers 125 and 127.. Theconnector switch is also controlled by the calling subscriber through the medium of the vertical and rotary'line relays 128 and'129. The vertical line relay I I 128 directlv controls the vertical magnet 130 and also the "rotary magnet 131. The office; ;o:E the verticahmagnet' 130 is to give the shaft and shaft wipers their yerti'cal motion,

and the rotary riuagnetltli imparts to the shaft and shaftwipers a rotary or'circular 134, and a so the side switch'wipers 135, 136,

138 and139. The side switchof the connector, like the side switch of the first-selector, has a normal or first position, a second position and a-third position. The release magnet 134 is also controlled by a special release relay 132. The central office is equipped with busy-signaling apparatus of any suitable design comprising an interrupter in series with the rimary winding of'aninduction-coil as s own at N, whereby a busysign'alingc'urrent is induced inthe secondary winding 260 of the said coil.

The line switch I (Fig. .3) tion of the line switch C (Fig. 1), and is bridged across the trunk conductors 192 and .193. Like the switch C it is equipped with the trip magnet 140'for operating the plunger arm 146, as explained 1n connection with the line switch '0. Also, the usual release magnet 141 provides the means. for restoring the switch to normal gosition. In this switch the cutoff relay 144 is provided with only two springs, namely 142 and143, which are arranged sothat when the trip magnet energizes and permits the'plunger to seize an idle trunk, the bushing 145 on the end of the plunger arm 146 then carries the spring 142 out of engagement with the spring 143, thus breaking the circuit of the trip magnet 140. The plunger arm '146 is similar to the plunger arm 450i the line switch C (Fig. 5), and in addition to thearrangement shown in Fig. 5 the bushing 145 is provided for hp crating the springs 142 and 143, as explained. The line switch K which is the terminal o the trunk line, the conductors 192 and 193 of which line are shown, is a modification of the switch C, and comprises the usual trip magnet 147 and the release magnet 148. but 'thebridge-cutofi' relay is omitted. Both of the'li'n'e switches K and C being allotted to the line of substation A, the switcbli may be termed the incoming switch and the switch C the outgoing switch, since when the substation A is called the line switch K is employed i'n establishing the connection, andwhen the subscriberat substation A callsanother substation the line switch C is-ln'ought into service. It will be understood, of course, that the substation A (Fig. 1) is provided with aswitch similar to the switch K,'in which switch the normal conductors 93, 94 and 96" terminate, exactly as the conductors 266,267 and 238 of the switch C" (Fig. 4) terminate in the switch K. It will alsobe evident that the conductor 95 pi the switch 0 (Figs. 1' and 5) terminates in a connector bank. exactly as-the conductor 207 of the switch C terminates in the bank of the connector H (Fig. 3).

is a modifica- A clearer understanding of the operation of my improved system may be obtained by considerin its operation when one subscriber cal s another. Assume, for example, that the subscriber at substation A desires to call the subscriber at substation A to which is allottedthe line #2220. To call the number 2220 the subscriber at substation A raises his receiver from the switch-hook and opcrates the calling device once, in the wellknown manner, for each digit. When the dial is rotated for the first digit a preliminary impulse is transmitted over the rotary line conductor. This preliminary impulse energizes the trip magnet 47, whereby the line switch is operated to seize an idle trunk lineleading to a first-selector. The dial in returning to normal position for the first digit operates the first-selector switch to establish. connection with an idle trunk line leading to a sccond-selectoiu' The secondselector F. in a similar manner, operates in accordance with the second digit to select an idle trunk line leading to a secondary line switch. \Vhen the dial is rotated for the third digit this secondary line switch receives apreliminary impulse and is tripped in or operated toscize an idle trunk lee loading to a connector switch H in the same manner in which the-first line switch C is o. crated to'seize a first-selector switch. It will be understood, ofcourse, that when the dial is turned for each digit a preliminary rotary impulse is transmitted to the rotary line,-

which impulse, if a selector E or F or a connector ll 1s on the lme, is received by the rotary line relay of the switch while the side switch is in first position. This rotary line relay, of course, energizes; but since the side switch is locked in first position until the shaft is raised; is without effect. and'the switch is not operated until the dial delivers the 'rertical impulses. Said prel'in'linaryinipulse is effective only in (po nting theline switches. The impulses i or the last two digits are directed toward the connector: ll which operates toplace lts sha'ft w-ipers'in connection with the contacts corresponding to the desired line, and when this connection is made the master switch M is operated to carry the plungers of all idle switches K opposite the trunk line leading tothe particular line'switch I previously. selected by the selector F. When the plungers are carried to this position the line switch K is tripped into connection with the trunk line conductorsl92 and 1.93, and the connector H autowgmatically released, whereby the conductors from the. second-selector are extended directly through the line switch K to the called substation. From this it will be evident that theconnector switch H merely serves to operatethe line switch K, so that the conductors from the second-seleetor are extended to the calling substal ion directly through the line switch K, and not through a connector. The preliminary impulse for operating the line switch C, which occurs when the calling subscriber rotates the dial in a forward direction for the first digit, is caused by the rotary impulse spring 24 being pressed against the ground post 20. As a result of the impulse the trip magnet 47 of the line switch 0 is energized by a flow of current through the winding of the motor mag-- net 71 to the battery lead 160, thence through battery B to ground Gr. Although this circuit includes the motor magnet 71 this magnet .71 does not operatively energizc, since the magnet 47 is of much higher resistance than the. magnet 71. As soon as the trip magnet 17 energizes, the armature 51 is attracted and theTplunger 4:1 is liberated and thrust into thebank terminal by the spring 5S, assuming that the plunger 4.4 is opposite the terminal Q, at the time. When the plunger Hengages the bank terminal Q an energizing circuit is closed through the motor magnet relay. 73,

which in turn operates to close an energizing circuit through the motor magnet 71.

all idle plungers which are in, engagement with the shaft 60 opposite the next idle bank terminal similar to the terminal Q. The cir- The motor magnet then operates toadvance cuit through the .relay 73 extends fromground G through the winding 161 of the relay 73, segment 74, wiper arm 75, segment 84, conductor 162, bank terminal springs 70 and 69, release magnet 48 to the battery lead 160. thence through battery B to ground G.

Although this circuit includes the release magnet 48 the magnet 48 does not operatirely energize, since the windings of the relay 73 are of a high resistance,"while the winding of the release magnet is comparatively low. The relay 73 upon energizing operates to place the springs 87 and 88 in contact, whereby a circuit. is completed through i the motor magnet 71 extending from ground G through the springs 88 and 87, motor magnet. springs 86 and 85, through the. motor magnet 71 to the battery lead 160, thence through battery B to ground G. The motor magnet-71 upon energizing attracts its armature 81, whereby the awl 82 engages the ratchet wheel 72 an rotates the wheel one step. When the armature 81 is attracted against the magnet cores the springs 85 and 86 disengage, thereby breaking the energizing circuit through the motor magnet. The cam 76 bein in engagement Rvith the in 77 is operat to advance-the plunger s aft 60, and consequently all idle nine subscribers have cal plunger-s that may be in-normal condition with the shaft 60, one step and to a point opposite another trunk terminal similar to the terminal Q, assuming the next succeeding trunk is idle. Consequently, the wiper 75 is carried from the contact. point. 84', which corresponds to the terminal Q, to the contact point 89, which latter corresponds to. the terminal before which the advanced idle plungers are now resting. Suppose that ed, and that the master switch has been thus operated nine steps, carrying the wiper 75-to the last contact point 164. Now, when'the motor magnet 71 0 rates for the last step, when the tenth su scriber calls, thewiper 75 moves back and drops into engagement with the con- 'tact point 84, as already explained. 'If the mg circuit first trunk is still busy the wiper 75 finds a potential on the contact 84, and an energizis established through the differential relay 73, which in turn operates to close an energizing circuit through the motor magnet 71. The' current through the said relay 73 flows from the said contract 84 through the wiper 75 to the comlnon segment 74, through the winding thereby-closing an energizing circuit'for'the .161 of the difl'erential.relay 73 toground Gt When the difierential relay 73 attracts its armature the differential relaysprings 87 and 88 are pressed into contact, 3

motor magnet 71'from ground .G throu h i the said springsr88 and 87,-.thiongh t e 86 and 85, motor lead 160, 'The motor magnet springs magnet 71, thence to the battery andthroughbattery B to groundG.

motor magnet then operates, as previously 40* one step, and the master switch bankwiper 60, when thus advanced one bank explained, to rotate the ratchet wheel 72 onestep for advancing the plungershaft 60 7 5 one step also, and into enga ement with the second segment 89. The p anger shaft step, carrisf all idle plungers that are in engagement {with the said shaft opposite the next bank terminal, as previously explained. If there shouldstill be a guarding potential at the ent 89 of the master switch bank the di erential relay 73 will remain energized," whereby the energizing circuit.

. throu h the motor magnet 71 is again complete when themotor magnet spring$y85 and 86 again engage; and as a result the motor magnet 71 is againpperated, whereby the plunger shaft 60 and t e master switch wiper 75 are advanced another step. This process continues as longsas the' wiper 75 continues to find segments with guarding potentials. Assoon as an'idle segment is found, however, the energizing circuit through the difierential'relay 731s broken,

nt'u'hiclrtime the said relay in turn breaks the energizing circuit for the motor magnet 1, until the next subscriber makes a call.

At the instant that the plan er l enters the said bank terminal Q t e following springs are pressed into contact: 63 and 64, 65 and 66, 67 and 68, and 69 and 70. The

engagement of the springs 67 and 68 cloths m a circuit through the cut-off relay 46 ex-.'

tending from ground G through the springs 68 and 67, conductor163, relay 46 to the bat tery lead 160, thence through battery B to ground G. The said relay upon energizing breaks the contact between the spjrmgs15l,

155 and 157, whereby the vertical and rotary line conductors 31 and, 32 become disconnected from the trip magnet 47. Thej-c'ut-ofi relay upon energizing places the springs 158 1 and 1:59 in contact, thereby esta lishlng a guard ng potential by way of the normal conductor to the connector private bank. contacts corresponding to the line that terrevent any 35 ininates in the line switch C, to subscriber from calling the suit line after the calling subscriber at substation A operates his dial preparatory to making acall, as explained. The circnitover which the said guarding potential is established ex- 90 tends from ground (ifthrough the spr ngs 159 and 158 to the private normal condom tor 95. Also, the closure ofconnection be-l tween the springs 69 and70 establishes a bank contact 84 over the following circuit:

Iftom battery B to the--battery 'lead 160,

through the release magnet 48 and-springs 69, and 70 over the conductor 162 to the said contact point 84. It will be understood that 106 the bank terminaLQ, being the first bank termirlal of the line switch bank, corre-' spond to the first segment 84 of the master switch bank 0 and, therefore,-to the trunk line, the conductors 90, 91 and 92 of which terminate in the selector E. This guarding potential. protects the seized trunk conductors 90, 91 and 92 from being seized by other plungers,asalready explained. The closure. of connection extends the calling 'subscribers'vertical line conductor 31 to the vertical trunk conductor 90 and to the side switch wiper 100 of the first-selector E. The closure. of contact be tween the springs 65 and--66 in a similar manner extends the subscribers rotary'lineconductor 32 to the rotary trunk conductor 91 and to the side switch wiper 101 of the selector E. The subscriber has thus establishedlconnection with the selector E which is now operated by the impulses that are sent .in as the dial returns. The first digit being 2 the spring 23 1s pressed onto the ground.

post. 20 twice. As a result the vertical lin'e rclay;108 of tl1e "firstselector E isenergized early-time by a flowiifc'urrent from the sub- 1 start on ground G throngh the springs 18 and 19 to the ground post 20. thence through the spring '23 to the vertical line conductor 31, line switch ba'nk springs 63and 64,11

guarding potential at the master switch 95 between the springs 63 and 64. 110

battery lead ltitl'and through battery 13 to vertical trunk conductor 90, side switch wiper 100 of the selector E, contact point 170. vertical line relay 108 to the battery lead 160. thence through battery B and to ground (1. Each time that the vertical hne relay 108 energizes, the line relay spring 111 is pressed onto the ground spring 110. The vertical magnet 9f) is thereby energized and the wipers 119, 120 and 121 of the selector 1) are raised tothe second bank level opposite the first contact of said level. The energizing circuit for the said vertical magnet )(3 extends from ground G" through the rings 110 and 111, private springs 10? and 1'06 to the vertical magnet 96, thence to the ground (i. The sprin 24 is then pressed onto the ground post 20. grounding the rotary line conductor 1"! and. therefore. ener gizing the rotary line relay 10E) of the selector It. The. energizing current passes from ground G to the rotary line conductor 2-32. thence it flows through the line'switrh bank springs 35 and (H3, rotary trunk eonduclor 91,- side switch wiper lUl oi' the selector ll, contact point in to the rotary-line relay 101i. thence to the' battery lead 160, and through battery B to ground. (i. The rotary line relay upon operating presses the line relay spring 112'onto the ground spring 110, thereby establishing a circuit through the pri\ate magnet 99 from ground through the sprlngs 110 and 112 to the private magnet 99. and through the said magnet to battery lead 1(iO. thence. through battery B to ground t.

I upon energizing and dei nergizing permits the selector side switch to pass from first to second position. permitting the side switch wipe s .102 and 103 to engage the contact points 172 and 17?). respectively. The closure of connection between the side. switch wiper 102 and the contact point 172 sets up an energizing circuit for the rotary magnet 97 from ground (i to the contact point 172. through the side switch wiper 102. interrupter springs 107, rotary magnet 97 to the battery lead 160, nd through battery B to ground G. The said rotary magnet {)7 then operates to?- -otate the wipersllt), 12$) and 121. of the. lector E into engagement with the first contact of the second leve] of thc selector banks, from which contacts, it is assumed the'trunk line conductors 175, 176 and 104 lead to the selector F. If the first trunk is busy, however, the wipers have to pass over busy trunk lines, and then as soon as the private wiper 121 engages the first groundedprivate bank contact point, the private magnet 99 energizes again, loclc ing the. side switch in second position. The energizing circuit for said private magnet shown) to the private wiper 121, thence over The n'ivate ma net the conductor 17-1 and through the back release relay 115 to the side switch 'wiper 103, contact point 173, private magnet 99, thence through said magnet to the battery lead 160', and through battery 15 to ground (i. The private magnet 99 upon thus be coming energized locks the side switch wiper 102 in engagement with the grounded con tact point 17!, whereby the rotary magnet 97 will be energized intermittently until the wipers arecarried beyond the last busy trunk line. At the instant that the private wiper leaves the last busy contact point the energizing circuit through the private magnet 5)!) is destroyed. and as a result the selector side switch passes to third position. lt. however. there are no busy trunk lines, the armature oi the rotary magnet 7 releases the side switch to third position as soon as the. wipers are carried into engagement with the first trunk line. As soon as the sideswitrh passes to third position, as stated. the subscribe1"s line conductors 31 and iii are extended to the colulurtors 173 and 17h. which in this case. it is assumed. lead to the selector switch 1*. The extension oi the line occurs. of course. as soon as the. sideswitch wipers NH) and 101 engage the contact points 177 and 178. respectively. Not only isthe subscriber-s line thus extended. but a guarding potential is also es tablished at the private wiper 121. when the side switch wiper I03 passes onto the grounded contact point 17 for protecting the seized trunk line from interference. by other calling subscribers. This guarding potential extends lrom ground (i to the .eonlact. point 179, thence through the side switch wiper 103. back-release. relay 115,- aiulronductor 17-lto the private wiper 1'21. It will be evident, of course, that the energizing.circuit tor the rotary n1agnet 97, to which reference has alreadv been trunk line is seizedthat is, when the side switch wiper 102 l aves the contact point 172. The second digit oi the called number being 2. the calling subscriber ope-rates his dial arcordingly as a result grounding the verticalline conductor 31- when the spring 21") meets the ground post 20. The vertical li'nerel-ay 188 of the switch F is. tlwrefore. emu'gized twice by a How of current t'roni the substation ground G to the vertical line, conductor 3], thence through the line switch bank springs'63 and (it to the vertical trunk conductor 90. thence to th'e'side switch wiper 100 of the selector 1*), contact point 177. ve.r-, tlcal line wiper 31:], vertical trunk conductor 17:"), side switcl. wiper 1.87, Vertical line relay 188 to the batterv lead 160. thence through battery B to ground G. That is, when the vertical line conductor 31 is grounded for thei'second digit the vertical line-"relay 18S operates to close a circuitthrough the erti mad-e. is destroyed when the idlethe Bear terminals cal magnet 264, which operates to carry the shaftlwi ers step by etc to a point opposite the second level. When the rotary line conductor 32 is grounded after the vertical impulses the rotary line relay. 206 is energized, whereby an energizing circuit is established through the private magnet 123, which in turn operates 1n the usual way to release the side switch,

as described in connection with switch E..

After the switch F comes to rest its shaft wipers 189 and 190 are in engagement with the trunk conductors 192 and 193,

re'spectively, which lead to the line switch I (,Fig. 3). The private wiper 191 estab lishes a protecting potential at the contact 194 for guarding the seized trunk line.

. Furthermore, the trunk conductors 192 and 193 terminate in the bank of the line switch K. Now, when the, dial is turned clock-, wise for the third digit the preliminary ro- 1 tary impulse, as previously explained, ener--' gizes the tripmagnet 140 which operates, as explained in connection with the line switch C, to seize a trunk line leading to the connector H. The energizing fill 6111i, of the trip magnet 140 extends from the substation ground G .to the rotary line conductor 32, trunk conductors 91., 17 6 and 193 to the conductor 165 (Fig 4), then'to the conductor 165 "(1*'ig. 3), through the cut-off springs'142 and 143, through the trip mag- .net 140 to the motor magnet springs 166 and 167,.through the motor magnet 168 to the "battery lead 160, and through battery B to ground G. The trip magnet upon energizing operates to permit the plunger arm 146 to trip-in, whereby the springs 180 and 1 81, 182 and 183, 184 and 185, and 186 and -18? engage. When the plunger arm 146 operates, the cut-0if spring 142 is carriedout o engagement with'the spring 143 by the bushing 145 upon the end of the plunger arm 146. The. disengagement of these springs cuts oiftheconductor 165 .from the trip magnet 140. -When the springs 182 and .183 are carried into engagement by the r of the switch 'I, an energizing circuit 1s established through the motor relay 195 of the master switch J. This circuit explunge tends "from-ground (it through the said relay, common segment 196 of the bank of the-master switch J and wiper 197 to the segment 1.98, then through the bank springs 183 and 182,- through the winding of the re lease'mag net- 14.1 to the battery lead 160.,

I and through battery B to ground G, The

"through the motor magnet 168.

relay .195 now' energizes and operates to "0' close the springs 199 and 200 in contact,

whereby an energizing circuit is closed Although the release magnet 141 is included in the en w-rgizing circuit of the motor magnet relay 105 it does not operate, since the rela 195 is wound to a high resistance, while the release magnet 141 is wound to a compara tively low resistance. The motor magnet 168 upon energizing operates the plunger shaft, as explained in connection with'the line switch C and the master switch D, :to 79 carry the engagin plungers opposite e next idle trunk line' which leads to a second connector switc Whe .theobank springs 180 and 181, anl 186 and 187 engage, the calling subscribers line conductors 31 and 82 are extended to the connector trunk conductors 201 and 202. The ground impulses 'from the substation to the line conductors for the last two digits-namely the third and fourthare directed toward the connector H. F or the third digit 2 the vertical impulse spring 23 is pressed onto the ground post '20 twice, whereby an energizing circuit is closed each time through the connector vertical line relay 128. This circuit extends from ground G through the ground post 20, spring 23, line conductor 31, springs 63 and 64, trunk conductors 90,- 175 and 192, conductor 1,52, springs 180 and 181. vertical line relay 128 to the battery lead 160 thence through l'attery B to ground G. Each time that the vertical line relay 128 is'energized the line relay springs 203 and 204 are pressed into contact, thereby closing an energizing circuit each. time 95 through the vertical magnet 130 which operates in the usual manner one step at a time. The shaft wipers 125 and 127 are, therefore, raised two steps and brought opposite the' level in which are located the'ter- 100 minals of the conductors 205 and 207 that lead to the incoming and outgoing line switches of the called line. Of these conductors to conductor 207 is the private'normal conductor and leads directly to the spring 243 of the bridge-cut-ofi' relay 236 of the outgoing line switch C. This condoctor is adapted to be grounded and maintained so when the line #2220 is busy. either by being called or by calling. The conductor 214 may be termed the master switch starter and leads to the master switch M of the group to which the incoming in dividual switch K belongs, passing'through j' the motor starter relay 213 to When the connector sideswitc passes to third position it will be shown that by. means of this conductor the said motor starter relay 213 is connected in series with the private magnet 133, and through said 1 0 private magnet to the non-grounded pole of the battery. The said motor starter relay,

gas will be more fully eiplained, starts the masterswitch and the latter operates until the wiper 223 strikes the contact in which 126 terminates the conductor 210 which leads through the line switch I to the release relay 132 ofthe connector H, thus causing the ound G individual switch K of the through battery B to and, at the same time, tripping 1 v and spring 24, line conductor 32, trunk conductors 91, 176 springs 186 and 187.

and 193, conductor 165,

I through the rotary line relay 129 to the battery lead 160, thence ground G. The rotary line relay upon operating closes an energizing circuit through the private magnet 133, which 0 crates to release the connector side switch first to second position. The last digit being ID the calling device is operated', as previousiy described, grounding the vertical conductor 31 ten times and the ro' tar-,line conductor 32 once. The vertical 5 an 'rotary line relays 128 and 129 areoperated over previously'traced circuits. ow ever, when the line relay springs 203 and 204 engage, a circuit is closed through the rotary .ma-gnet- 131 instead of through the vertical magnet 130. Each time that'the rotary magnet is energized it operates to rotate the shaft and shaft wipers 125 and 127 one step at atime until the said wipers are carried. into engagement with the com ductors 205 and 207 which are allotted to the line of substation A. The energizing of the rotary line relay 129, as previously stated, completes an energlzlng circuit through the private magnet 133 which now operates to release the side switch from second to third position, thus placing the side switch wipers 135, 136, 138 and 139 in contact with their respective contact points. VVhenthe side switch wiper 135 engages the contact point'208 a ground potential is established at the, bank contact of the master switch M (Fig.4) corresponding to the con-,

ductors 192 and 193 of the trunk line. This potential extends from ground G at the connector H through the release relay 132, contact point 208, side switch wiper 135, conductor 209, bank springs 185 and 184, conductor 210 to-the segment 211 at the master switch bank, Fig. 4. The side switch wiper 136 upon engaging the contact point 212 closes an energizing circuit through the motor magnet relay 213 (Fig. 4) extending from ground G through the said relay 213, conductor 214, side switch wiper 136, release relay springs 215 and 216,

through the privjte magnet 133 to the battery lead 160,9. d through battery B to ground G. The relay 213 energizes and places the springs 217 and 218 in contact, whereby an energizing circuit is closed through the motor magnet 221 from ground G" through. the springs 217 and 218, motor magnet interrupter springs 219 and 220, through the motor magnet 221 to the battery lead 160, and through battery Bto ground G. As long as the connector H remains with the side switch wiper 136 in third position the energizing circuit through the relay 213 is maintained, and also the energizing circuit through the motor magnet 221. The motor magnet continues to operate, rotating the ratchet wheel 222 step by step until.

the wiper arm 223 is carried into engagement with the segment'211'which, as already described, is grounded through the release relay 132 of the connector switch H. As a result, when the wiper arm 223 engages the segment 211, an energizing circuit is closed through the release relay 132. This circuit extends from ground G at the connector H through the relay 132 and side switchwiper 135, as explained, to the segment 211, then through the wiper 223 to the common segment 224,, thence to battery lead 160, and through battery B to ground G. The relay 132 upon energizing operates to release the connector switch H and also the line switch I. Now \vhen'the connector releases, the side switch wipers 135 and 136 then leave their respective contact points 208 and 212, whereby the energizing circuits.

through the release magnet 134 of the connector H and through the release magnet 141 of the line switch I, it will be understood, are subsequently broken when the release relay 132 deenergizes and permits the springs 225, 226 and 227 to separate. It will be understood, therefiore, of the. connector switch H and of the line switch I occurs as soon as the wiper 223. of the master switch M engages the segment 211, the mechanism of the master switch being so, timed in its operation that therelease relay 132 of the connector switch has time to energize and to in turn energize the release magnets of the connector switch H and line switch I; and finally the motor that the releasing.

magnet relay 213 has time to interrupt the .motor magnet circuit before the master switch has time to operate and carry the wiper 223 out of engagement with the con- 

